In a seamless instrument panel having an air bag cover, a predesignated splitting line is formed so that the air bag cover is easily split when an air bag apparatus is activated and expanded on collision of an automobile.
Heretofore, an air bag cover has been formed with a soft highly impact resistant material even when it is accompanied with decrease in rigidity or heat resistance so that formation of pieces having sharp shapes can be prevented even when the air bag cover is broken at the time of the splitting.
It is also conducted that talc is added to a resin composition for an air bag cover so that some degree of rigidity is provided to the air bag cover. In general, fine talc (having an average particle diameter of 10 μm or smaller, in particular, 6 μm or smaller) exhibiting an effect of greatly improving heat resistance and rigidity is used.
As the air bag cover, an air bag cover molded from a composition containing polypropylene, an ethylene-α-olefin copolymer rubber and talc having an average particle diameter of 15 μm or smaller is disclosed. This air bag cover is used in combination with an instrument panel molded separately to form a single article (for example, Patent Reference 1).
Since the above resin composition for an air bag cover cannot have a great rigidity due to a great content of the rubber component, integral molding of an instrument panel and an air bag cover using this resin composition as the single material is not possible.
An air bag molded from a composition containing polypropylene, two types of ethylene-α-olefin-based amorphous copolymer, a propylene-1-butene copolymer exhibiting low crystallinity and a mineral oil-based softening agent is disclosed (for example, Patent Reference 2). The use of talc is described in the reference, but no descriptions can be found on the diameter of particles of the talc.
In Patent Reference 1, different materials are used for the composition for the air bag and the composition for the instrument panel.
Therefore, it is necessary for achieving the “seamless” condition of an air bag cover and an instrument panel that the air bag cover and the instrument panel be melt adhered for integration.
The above process for integration has a drawback in that the portion of melting tends to protrude from the surface.
When a material for a face film is inserted into a mold to attach the face film to the outer faces of an air bag and an instrument panel, problems arise in that the face material moves in the mold and wrinkles are formed on the face film. It is the real situation at present that this process cannot fully satisfy the requirements in the market.
Since the composition for an air bag and the composition for an instrument panel are different materials, the composite product cannot be treated as a single article in recycling.    Patent Reference 1: Japanese Patent Application Laid-Open No. Heisei 10 (1998)-273001    Patent Reference 2: Japanese Patent Application Laid-Open No. Heisei 10 (1998)-279745